A known variable valve timing control apparatus, where a relative rotational phase of a driven-side rotating member rotating integrally with a cam shaft of an internal combustion engine relative to a driving-side rotating member rotating synchronously with a crank shaft of the internal combustion engine is controlled, includes a fluid pressure chamber formed between the driving-side rotating member and the driven-side rotating member, and a partition provided for partitioning or separating the fluid pressure chamber into an advanced angle chamber and a retarded angle chamber. According to the known variable valve timing control apparatus, switching between supply and discharge of working fluid relative to the advanced angle chamber or the retarded angle chamber is controlled, and thus the relative rotational phase of the driven-side rotating member relative to the driving-side rotating member is controlled. The above-described technique is disclosed in, for example, JP2008-275093A (hereinafter referred to as Patent reference 1).
A known valve timing changing apparatus (corresponding to the above-described variable valve timing control apparatus) disclosed in Patent reference 1 includes a rotating body (corresponding to the above-described driven-side rotating member) and an outer side rotating body arranged at an outer side (corresponding to the above-described driving-side rotating member) which are arranged coaxially with each other, and two fluid pressure chambers which are supplied with working fluid via respective two fluid pressure passages. The valve timing changing apparatus changes a relative rotational position of the rotating body and the outer side rotating body relative to each other on the basis of fluid pressure of the two fluid pressure chambers, and thereby changing a valve timing of a intake valve or an exhaust valve of an internal combustion engine. According to the known valve timing changing apparatus disclosed in Patent reference 1, the rotating body is arranged at an outer periphery of a substantially column-shaped body axis to be coaxially with the body axis. The two fluid pressure passages are connected via respective inner passages of the body axis to respective annular passages formed between the body axis and the rotating body. Further, seal rings partitioning the respective annular passages of the two fluid pressure passages are disposed between the axis body and the rotating body, and ring grooves each of which is recessed to have a substantially rectangular cross section are formed at an outer circumferential surface of the body axis or an inner circumferential surface of the rotating body. The seal rings are arranged at the respective ring grooves in a manner that each of the seal rings enters the corresponding ring groove.
According to some of the variable valve timing control apparatuses, before a start-up of the internal combustion engine, the relative rotational phase of the rotating body and the outer side rotating body relative to each other is fixed at an intermediate position between a most retarded angle and a most advanced angle before a start-up of the internal combustion engine, and the relative rotational phase is controlled to move to the most retarded angle-side or the most advanced angle-side after the start-up of the internal combustion engine. However, the intake valve or the exhaust valve of the internal combustion engine of which relative rotational phase is controlled by the variable valve timing control apparatus is pressed downwardly (or pressed upwardly) against a valve spring, and therefore an intake timing or an exhaust timing may possibly delay relative to a desired or intended timing. In this case, an operation of the internal combustion engine may deviate from a desired or intended operation. Thus, after the start-up of the internal combustion engine, it is required that the relative rotational phase be controlled to move quickly from the intermediate position to the most retarded angle-side or to the most advanced angle-side.
For example, the technique described in Patent reference 1 may be applied to the above-described variable valve timing control apparatus. The variable valve timing control apparatus is configured so that the supply and the discharge of the working fluid are conducted, and that a pump provided at a supply path of the working fluid of the variable valve timing control apparatus pumps up the working fluid from an oil pan. Accordingly, depending on a flow path resistance of the supply path, the working fluid may not be supplied to the variable valve timing control apparatus immediately after the pump starts. On the other hand, a discharge path of the working fluid of the variable valve timing control apparatus is configured so that the working fluid returns to the oil pan freely without intervention of, for example, the pump. Thus, according to the configuration of the variable valve timing control apparatus, the flow path resistance at the discharge path is set to be relatively low, and thus the working fluid is discharged easily (that is, a drainage performance is high). Because of the above-described configuration where imbalance exists between the flow path resistance at the supply path and the flow path resistance at the discharge path, the working fluid may not be supplied smoothly to one of the advanced angle chamber and the retarded angle chamber in order to move the relative rotational phase from the intermediate position to the most retarded angle-side or to the most advanced angle-side. In this case, it is difficult to move the relative rotational phase of the rotating body relative to the outer side rotating body to the desired or intended relative rotational phase, and therefore it may take time for transition to the desired rotational phase to take place. Consequently, the operation of the internal combustion engine may deviate from the desired or intended operation.
A need thus exists for a variable valve timing control apparatus which is not susceptible to the drawback mentioned above.